Small gasoline engines power a wide variety of lawn and garden equipment such as lawn mowers, lawn tractors, chain saws, and so forth. In such engines, an air cleaner filters out grit from air entering a carburetor to prevent dirt from getting into the engine, where it would cause excessive wear of moving parts. The air cleaner may have one or more filter elements which must be cleaned or replaced periodically. For instance, most manufacturers suggest cleaning or replacing the filter after every 25 to 50 hours of engine operation, but if the engine is operated in an unusually dusty or sandy area, service of the air cleaner should be performed at even shorter intervals.
Air cleaners typically include paper, foam, or metal air filters. Such filters eventually become clogged, making the engine difficult to start and may cause the engine to stall, run hesitantly, or overheat. Chain saw filters can clog after being used for less than 10 hours.
Most air filters for chain saw engines are located toward the top or rear of the engine, and are either attached directly to the carburetor or connected to it by a short adapter. One conventional air filter, for example, includes a bowl with a layer of oil therein, a filtering element within the bowl with a lower perforated surface thereof facing the layer of oil, and a cover fitted over the filtering element and the bowl such that air enters through an opening between the cover and the bowl, passes between the filtering element and the bowl, then passes upwardly through the lower surface of the filtering element and downward through a pipe at the center of the bowl.
Another conventional air filter includes a metal housing having a lower wall with openings therethrough, a foam filter supported within the housing, and a pipe passing through the foam filter with a lower end of the pipe in fluid communication with an opening through the bottom wall of the housing. The foam filter overlaps the upper edge of the housing and a cover clamps the foam filter against the housing. Air enters the openings in the lower surface of the housing, passes upwardly through the air filter and then downward through the pipe and into the carburetor.
A third type of conventional air filter includes a paper element and a foam sleeve fitted around the paper element. This type of filter includes a lower plate having an opening therethrough in fluid communication with the carburetor and a cylindrical cover which clamps the foam sleeve and paper element against the lower plate such that air passes through an opening between the cover and the lower plate, passes through the foam sleeve, then through the paper element and then through the opening in the lower plate.
Each of the three types of air filters described above includes a bolt passing through the cover for purposes of attaching the cover to the air filter assembly. With such arrangements, dirt can find its way through the opening in the cover and lead to engine problems. Accordingly, there exists a need in the art for a air filter assembly which eliminates the problem of dirt entering through the cover of the air filter assembly.